Central’s PREP has a grid-tied photovoltaic (PV) system that uses Ten K Solar panels connected directly to the distribution grid.
Central’s PREP has a grid-tied photovoltaic (PV) system that uses Ten K Solar panels connected directly to the distribution grid.
Central’s PREP has a grid-tied photovoltaic (PV) system that uses Ten K Solar panels connected directly to the distribution grid.
Central’s PREP has a grid-tied photovoltaic (PV) system that uses Ten K Solar panels connected directly to the distribution grid.
Central’s PREP has a grid-tied photovoltaic (PV) system that uses Ten K Solar panels connected directly to the distribution grid.

A Microgrid to Power the Future

March 27, 2017
Central Electric Cooperative constructs the infrastructure to support a business park that contains a microgrid to ensure reliability.

In this age of technological advances and the internet of things, customers expect a higher level of service. This new customer expectation and the exponential change in technology will have the electric power industry seeing more change in the near future than has occurred over the past several decades.

Confronting change is not new to Central Electric Cooperative, a distribution cooperative that serves more than 20,000 meters in north-central Oklahoma, U.S. A large percentage of the cooperative’s load is oil and gas — an industry known for volatility and its boom or bust nature.

“The utility industry is beginning to experience very disruptive forces,” said Central CEO David Swank. “Central has experience facing disruption from the oil and gas industry, and the board of trustees has been instrumental in allocating resources to confront this disruption with innovative technology solutions.”

Distribution management has changed significantly over the past few years as utilities are being affected by multiple forces such as new regulations, disruptive technologies and changing load characteristics. With a mission to provide safe, reliable and affordable power to its members, Central began looking for solutions to help the cooperative better manage its distribution system more efficiently.

Central recognized the need to gather and analyze data in real time to make more educated and timely decisions, which were essential to managing the growth Central was seeing on its system in 2012. An abundance of data from multiple utility systems and intelligent electronic devices required Central to re-examine its need for secure, adequate data storage and a strong communications backbone.

Central Electric Cooperative worked with an ecosystem of partnerships, including Today’s Power Inc., to support engineering and execution of the PREP. The solar array was made possible through a U.S. Department of Agriculture grant.

First Steps

In 2013, Central built a modern systems operation center (SOC) with technologies integrated to monitor oil and gas load in real time. The SOC helped the cooperative increase reliability and reduce costs. That same year, Central also installed its first hardened data center to house the utility’s data securely on site. After installing fiber to all its substations, the cooperative worked with a local internet service provider, ProValue.Net, to expand a wireless network across Central’s seven-county service area. The hybrid fiber and wireless network connects the SOC and data center to intelligent electronic devices in the field.

A New Infrastructure

In 2016, Central constructed a new facility and the infrastructure for a business park/micro-community called Innovation Pointe. The campus shares various technologies, including an expanded state-of-the-art SOC and a Tier II data center, located in a hardened area inside Central’s new headquarters. Maximizing reliability and uptime was a priority in the engineering and design of the campus.

The cooperative is using self-healing grid technologies along with Open Systems International’s distribution management system with fault location, isolation and restoration (FLIR) to increase service reliability and decrease costs associated with prolonged outages. Central is confronting today’s energy industry challenges by using research and technology to develop a more modern and resilient grid.

Resiliency is also achieved with a combination of energy sources from an on-site Progressive Resource Energy Park (PREP). The PREP design uses existing grid resources interconnected with new renewable energy and battery storage technologies to power the campus. The PREP played a large role in the new building achieving LEED Gold status by the U.S. Green Building Council. The building achieved the maximum points available in the categories of optimize energy performance and on-site renewable energy.

The systems operation center is used to monitor day-to-day utility operations as well as the output of Central’s PREP.

Powering Up

Central’s PREP has a grid-tied photovoltaic (PV) system that uses Ten K Solar panels connected directly to the distribution grid. The PV system provides power for the campus and excess power is provided to the distribution grid. The system is rated at 504 kW AC with a 1.366 DC-to-AC ratio, and is configured along a north-south orientation.

A battery energy storage system (BESS) is used in the PREP to mitigate the impact of solar intermittency. Changes in PV power production can exceed 50% of the clear-sky generation potential over a one-second interval. August and September data shows a maximum 425 kW/s rate of change. Central used the Tesla Powerpack product to maximize the use of renewable energy. The PREP BESS is rated at 250 kW/475 kWh and consists of five battery packs. Each battery pack is rated 100 kW and includes a DC combiner panel, bidirectional inverter and a site master controller.

A diesel generator rated at 750 kW was installed at the PREP for backup generation. The generator was sized to take into consideration peak load of the campus, single-phase loads and load imbalance, uninterruptible power supply, variable-frequency drives, voltage and frequency dips during start-ups, and future expansion. With all these considerations, the generator is sized to pick up all loads in one step, with the ability to satisfy the campus demand peaks, even in the absence of solar power and a fully discharged BESS.

Central employees look at the interconnection equipment that connects two substation feeders, solar, battery storage and the Innovation Pointe load.

Controlling the Campus

Switchgear is tied to the grid fed by two of Central’s substations. Two series of three each SEL-651R recloser controls are used for feeder protection with one each near the campus. The design criteria require that only one of the two reclosers is closed at any instant. The Vista Switchgear is designed to be connected to either substation feeder. Based on the design changes and operational requirements, the traditional fuse-saving scheme employed in Central’s system had to be disabled.

Under normal operating conditions, one of the substation reclosers is closed, and the other recloser is open. If the feeding substation faults, the other substation recloser will close. Isolating renewable sources for any fault in the system plays a significant role in designing the Real-Time Automation Controller (RTAC) and communications schemes. SEL-651R is configured for IEC 61850 Generic Object Oriented Substation Event (GOOSE) messaging using high-speed fiber communications infrastructure to transmit and receive messages from the RTAC. The RTAC is programmed for feeder reconfiguration schemes, fault isolation and dead-bus detection scheme to start the diesel generator in the event of total grid failure.

Net Zero

The ultimate goal is for the Innovation Pointe campus is to be capable of off-grid operation. A short-term goal is for the new headquarters to be net zero, which was achieved during the first six months of operation because of the solar generation. The microgrid has mitigated an outage for 739 Central members to just a few seconds. The microgrid self-healed the campus location to the alternate feeder within 12 cycles preventing a 110-minute outage for members and the Innovation Pointe campus.

Load-duration curve shows photovoltaic contributions to battery charging and grid load decrease.

Next Steps

As the Innovation Pointe campus continues to grow, Central has identified several objectives for the PREP:

  • Monitor peak shaving with the battery system and diesel generator to discharge at times of peak demand to avoid or reduce demand charges
  • Enable emergency backup from the BESS to provide intermediate bridging power to the park in the event of grid interruption
  • Integrate solar forecasting into building automation system operations to reduce load requirements during low solar production
  • Incorporate knowledge feedback into the design cycle to improve design decisions.

“The PREP engineering model is providing value to the entire membership,” said Swank. “Beyond the benefits to reliability, the PREP model provides sustainability for the future of Central as renewable energy begins to challenge the traditional utility model.”

This chart shows the net energy usage of the PREP and the Innovation Pointe campus.

A Laboratory for the Future

The Innovation Pointe campus will serve as a laboratory to design and implement smart community resources within a micro-community setting. A key component of this laboratory is the continued training and development of employees.

“As Central moves beyond traditional utility functions, it is important for employees to have the leadership and technical skills that enable the cooperative to bring ideas such as the PREP to fruition,” said Swank. “Our employees, and specifically the line personnel, have taken the initiative to learn new technologies that are instrumental in installing and maintaining the PREP.”

The micro-community laboratory allows for the engineering, testing and implementation of various technologies, and offers a better understanding of how these technologies can be optimized in larger settings. Ultimately, the PREP engineering model enables technologies to be scaled to residential, commercial, and industrial parks with the potential to scale to an entire community.

Central was recently recognized by the Oklahoma State Regents for Higher Education for its partnership with Oklahoma State University. The Business Partnership Excellence Award highlights successful partnerships between higher education institutions and businesses that cultivate higher learning and further the education of Oklahoma’s workforce.

This image illustrates the elements of this laboratory setting at the Innovation Pointe campus.

A Community Approach

Central has created a limited liability company called Smart Energy Source (SES) to help propel Central as a next-generation utility. Through SES, an initiative called Smart Community Source was developed to serve as a catalyst to help communities with urban planning and developing resources. The cooperative wants to help businesses, utilities and communities implement energy management and execute PREP solutions that allow the entities to use energy more efficiently. As the energy industry changes, SES strives to be at the forefront by researching and developing innovative energy solutions

Innovation and collaboration are two attributes critical to Central’s success. The PREP solar array and a campus-wide geothermal loop were made possible through U.S. Department of Agriculture grants. The cooperative also has an ecosystem of partnerships to support engineering and execution through working relationships with Arkansas Electric Cooperative Inc., Automated Integrated, Edison Energy, Guernsey, Pro Value Net, Tri-County Electric Cooperative, Ten K Solar, Tesla Energy and Today’s Power Inc. ♦

Todd Hiemer joined Central Electric Cooperative as executive vice president of engineering in 2014. Hiemer has more than 10 years of electrical power engineering experience at both investor-owned and cooperative electric utilities. He holds BSEE and MSEE degrees from Oklahoma State University and an MBA degree from Oklahoma City University, and is a registered professional engineer in the state of Oklahoma. He is also an ABET program evaluator, a senior member of IEEE, an IEEE Power & Energy Society Region 5 representative and president of the Oklahoma Future City Competition Foundation.

David Freeman is the director of systems intelligence at Central Electric Cooperative. He has more than 20 years of experience in the utility industry, working in various roles in the operational, engineering and technology fields, and currently manages the systems operation center at Central to provide a data-driven solution to acquire and derive business intelligence strategies. Freeman holds a BS degree from Oklahoma State University.

Yuvaraj Kondaswamy is a system engineer at Central Electric Cooperative. Prior to joining Central in 2012 as a system planning engineer, Kondaswamy spent three years gaining electrical engineering experience at ESSAR Steel Ltd., India. He has experience in distribution system planning and protection, distributed generation interconnection studies, arc flash analysis, harmonic assessment and mitigation, and reliability analysis. He holds a BS degree in electrical and electronics engineering from Government College of Engineering, Tirunelveli, and an MSEE degree with a specialization in power systems from State University of New York, Buffalo. He is a registered professional engineer in the state of Texas and a member of IEEE.

Larry Mattox is the director of communications at Central Electric Cooperative. He began his career with Central in 2006. Mattox holds a BS degree from Oklahoma State University.

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